1996AJ....111.2349H THE 4 8 5 3 9 7 6 2 under 1 2349 16 15 14 13 12 "Department 'Ooepartment Department Kitt Department Based Division Department Washburn 0perated UCO/Lick The IPAC, Lowell US US © Peak Naval Naval ASTRONOMICAL NASA Observatories, Astron. on American Caltech, Observatory, of by J. JEROME A. observations interface We three the the range photoionization between shape conclude face-on object evidence globules globules is of globule" mass, refer that serious forming flows. onset More National Obs., Observatory, Observatory, Observatory, Geological of of of M. JEFF contract the of of that this BAUM, essential interior present Physics Physics Astronomy, photoevaporation J. Physics, Astronomy, to HUBBLE Dept. Association 100-22, principle FABER, generally, of of of thereby 111 as Photoionization structure in HESTER,2 Observatory, difficulties these Carnegie against KRlSTIAN,13 environment that observations the the stellar with 5-26555. and the 5 that 1400 connect interpretation M16 of with (6), and and and ARTHUR of Board Princeton Hubble P.O. 3450 Pasadena, Astronomical Astronomy, features 3 9 ionizing dense nebular are the ,4EDWARD structures FM-20, JOURNAL W. Astronomy, Astronomy, the Planetary stellar the CARL June the New results freezing of SPACE we of winds, Institution Box the we Massachusetts are of being Mars observed PAUL NASA/ESA Universities masses nebula National these with a Mexico 1996 molecular Studies are Space find University, 1149, backdrop found CODE, California photoevaporative University J. condensations objects of continuum. ROBERT Hill by of may of Sciences, 475 GRILLMAIR, of uncovered seeing as A. the TELESCOPE as the the Arizona University naturally that J. this of globules Flagstaff, H the supports Road, Optical State in of photoevaporative N. in evaporating Telescope 6 to have SCOWEN, offset SHAYA, Washington, competing II for observations, Hubble Astronomy DOUGLAS mass Ave., Charter disk-like stars study. nearby seen 91125. more Princeton, be of EMERGING regions. Received of M. material University, California Research the Flagstaff, State Society Washington, uncovered Astronomy a of the Arizona between NW, Interpretation LIGHT, accounts in in distribution Space as to the sensitive 7 objects 9 isolated St., Maryland, First, University, seen 2 KENNETH 0 EDWARD IR the WFPC2 the ionized ongoing and RAVI 813 Washington 1995 WFPC2 structures New view flow. Second, in "evaporating Madison, G. gaseous globules, gaseous Arizona Institute stars. 0004-6256/96/111 and Telescope, Las 86002-1149. images VOLUME 14 Astronomy, previously main cluster Astrophysics, the Santa including CURRIE, Observatories emission September Jersey Seattle, from many C. • Cruces, YOUNG for SANKRIT, that the regions function Photoionization flows College morphology Tempe, face © images Provided ROGER 86001. of Barbara J. ABSTRACT bodies Wisconsin IMAGING of P. star we the of interior DC. of 08544. much environment are the Technology, obtained 1996 GROTH, EGGs Washington SEIDELMANN, the 7 New the of may Inc. 111, M16 report Park, 21; G. properties formation, the peaks in Arizona of relatively side, disk" University 10 both 2 STELLAR St., the LYNDs, of of protostars , American interaction Mexico under of M42. EDWARD revised TOD star Box extremely NUMBER provide while 53706. ( Maryland of at elephant 6)/2349/12/$6.00 or Pasadena, the 10 or the molecular the and while the of in OF model 85287. the 26732, 170-25, 98195. by JON formation, in cooperative R. "EGGs." elephant models The lower the 88003. emission 1996 3 Space of discovery the in rare · stratified the 4 of M16: H including LAUER, 16 the California, A. DAVID a 20742. DANIELSON, in M16 Astronomical at density OBJECTS primary California Tucson, stellar of objects trunks II previously 6 February Pasadena. AND continuum localized useful in Telescope HOLTZMAN, and M42 an region of cloud. the NASA PHOTOEVAPORATION either trunks agreement are These from 3 but JAMES an early G. ionization higher .4 objects of Arizona photoevaporative in profile the Santa paradigm difference in EDWARD the 91101-1292. 20 generally empirical California MONET, rather a the Science is We nebula. 1 region H are both 8 population applied objects appear stage HST well association Crnz, SHAWN Astrophysics A. with II ionization Society. H 85726. 11 in find of dispersed. regions WESTPHAL II by DEIDRE nebulae, structure Institute, them the of images the 91125. California understood 15 for Third, in A. region determined density between to that to are disruption [S EARLJ. National P. their interface AJHAR, be interpreting the © were of II] may seen EWALD, the lines. which the of flow 1996 the A. themselves. M16. Several objects small while emission of 95064. profile evolution. 8 Science still the a "evaporating HUNTER, same arise data the O'NEIL, 3 more · in is Am. with The 4 AND number of not and Data There two WILLIAM 8 operated cometary accreting interface avoiding terms SANDRA in indicate lines the capture in type a Astron. Foundation. details by nearly gas of at M42. cases wide such 12 JR., star We We the are the the System of of of of in by JUNE AURA Soc. 1996 2349 Inc., 1996AJ....111.2349H region-M42 between from further low 2350 markably AU ture terms clear also diation driven Photoevaporation More the veloped by phasized interested generally in Zuckerman molecular regions. rative Baldwin tive mostly wide photoevaporative rative Orion less the much region overdense nent (e.g., elephant evaporation for ground interface-the limb-brightened into that tion low look tangency which "Eagle the The Photoevaporation Unfortunately, Bertoldi seminal structure a of of flows ionization © clearly shape and ambiguous the "elephant effects. for the range minimum Goudis recently of at of flow, context flows the the ''bar'' implosion HESTER M16. the from face-on, American discussed based first Nebula") by In photoionization the high some trunks that which forms et interface. blister-like the against thin; might clouds H gas in the regions H al. Kahn this (1989) of showed work and and 1973; H massive II might Hubble rather M16 the This H II is ionization 1976). images cross near (Hester of observations time photoevaporation evolving region/molecular same 1991; lines trunk" II a is in view ET seen so of viewing region/molecular instabilities complicated II account arcs, suggested entire as blister which (1969), region significant a might interfaces. is M42 by still Ml6 by more (NGC and confusion the the AL.: region in Pankonin than prove that relatively a the part of structures section originates sort M16 Rubin under 1. Oort stars Space a Astronomical the Hester mechanism and embedded observer the et structures. interface. Bertoldi surface INTRODUCTION provide molecular better is HST stratification gave H H models species. across be favorable of for of geometry and al. Sandford of heads 6611, not to II is is & evolution are II molecular that of a the an the et in IMAGING flow much regions Telescope region fraction an 1991a)-showed best The be due by birth larger of Spitzer (1991), the understanding an smooth et H bright of al. the which especially an it. photoevaporative from is & of photoionized S49, combined old cloud of This of important al. projection The II the within ideal the These molecular to that of cloud known material generally interface Even 1991). McKee ideal rocket-effect-driven these of to can regions. et H geometry clouds region problem, (e.g., background seen induced blister of 1979; or as the (1955) n emission in the within stratified have convex al. II cloud, of flow who background, should interface. OF location be the protrusions images viewing regions. interpretation more the interface structures well Society (1982), exciting the emission Hester for in Giuliani important (1990), MI6 found of effects broken by has in interpreted ionization effects. is away Peimbert in looking molecular cloud visible and of a which emission star surfaces several star dating allows photoevapora­ be a as popularly, ultraviolet interpreting structure few the M42 been photoevapo­ photoevapo­ for of The images The geometry It (1991) and and present further in radiatively flow formation. stars formation, from is who out of from from to appear 1979). has interface began studying an allowing light hundred A the through evolved • back process studied is seen a projec­ others. promi­ photo­ be of of struc­ of 1982; much away cloud flows from (e.g., Provided were been it H clear seen both was H em­ H de­ are the ev- re­ the ra­ the the the in to as In as in in II II II a between erywhere contains of Wide to stars sequence elephant of globules, globules, tions. We vironment, tinuing young photoevaporation Sec. structures given with The Trauger imaged Planetary trunk features trunk (Hester CCD CCD. an F656N Planetary these and (A.A. noise. tion using (F547M). difference ing ric resampling ( 1994). better In In star Figure the Two image solution by report an X 2 times 5. small with the 6717,6731), addition, this The Field in cameras cameras Three standard Mosaics photoevaporative formation. stellar algorithm A star (Ha et The the using the Wide many Sec. exposures understand et trunks a along stars 140 or in their scale brief Camera) The 1 Camera al. were paper photoevaporative the and number box between al. the formation. and (Plate elephant given of M16 two EGGs, 11.6563), NASA 6. seconds 199lb). seen 2. the objects discovery (Hillenbrand images M16 Field that young these records environment, in (1994). the data of summary of procedures shows 2 X 2 in Planetary OBSERVATIONS exposures we that particular on are By Hubble the and 0~ by M16. photoionized of 133) has protruding 2. image were is onto the are the PFUEI cameras 1 1100 present star 2.1 trunks the F502N which studying combined low M16 for The rejects Holtzman Astrophysics were a per (YSOs). the a an its The effect shows region discussed interface two of In result Observations a and largely formation F547M. obtained seconds Camera image Space pixel. and adjacent image region common WFPC2 is in as the et taken a Sec. on interface are and WFPC2 but new ([0 (the cosmic exposures a population famous into each al. of described the intermediate of of an effect the few AND known These face images in The H et scale 2 Telescope line III] massive Wide 1993). onto on the active along of The Hubble for Ha the 2 structure in Palomar tum II al. we filter in fields concluding in grid has RESULTS of (WFPC2) rays 11.5007), the remaining region is 1 that interaction has Sec. Ha, for interior free of each image (1994). images evaporating M16 to present April, a the Field are discussed were the with Data The star been using were n Holtzman in of nebula 0~046 Lora! be the they by of stars four Space [S 4. molecular continuum themselves Wide mass of 1.5 small surfaces we associated is of formation, Cameras) elephant view. constructed comparing II], large of The 1995. F673N the of combined were described have Figures the the observations the discussed on independent remarks m System 800 per four camera might M16 of the which and Telescope pre-main­ in Field computed cometary telescope astromet­ effect interface their observa­ elephant massive Each gaseous pixel. on Integra­ reduced nebula. Sec. X [0 cloud. of filters: ([S trunk taken hope et 2350 con­ have sites filter 2, with was and (the 800 and en­ III], the are the us­ by a!. by of in II] 3. of 3, 1996AJ....111.2349H III] blue. images, the stretch, and while 3 elephant field located 2351 to heads principle southwest ing implying 1978; tures the through presumably and Conversely, extinction what emission evidence lecular photoevaporated shows appearance of greater locations ley, ment indicates cations normal rest photoevaporation striations effects of in tant that material be X these The The the The the diverted images, the 10 same 4 from © sky. in which so of energy of and in (Plates of 16 of a outer clear HESTER the American Hillenbrand nucleus distance ionizing allowing the cloud view cause detail morphology is WFPC2 with to structures 3:5 front about 4 PC em, the Column trunk the in surrounding the from sources of that "above" that figure. 3.1 in and features presumably (left dynamics the H showed respectively. is by the illuminated striations columns pixel deposition Ha or parts elephant photoevaporation. ionizing [S of 134, M16 so of into in the II the much The it interface, Fig. the features which much. to of about the II] ET to interior region radiation Fig. both the one image images is Figure material of I flow pressure and of 135, right is as the Photoevaporative Ml6 the properties shown 3. against point AL.: 5 WFPC2 in being shows 2.2 similar like ionizing of of ionizing et PHOTOEVAPORATION the columns 1.3X 6 II Astronomical WFC faint (Plate volatile trunks. stars pointing the This 6 the interior the comet. and somewhat lines al. (Plate the (cf. at in the and of HST Basic across X is on of regardless that 5 flow of The normally upper as the illuminated 10 or related nebula. WFPC2 10 the is approximately and the emission appear gradient flow shows is 136) emission the Dyson their striations Ill 1993). pixel Ml6 covers 137).) IMAGING red, 18 in 15 of (The orientation streaming stars. consistent materials displays radiation of 138), or interface I, Geometry head This nebular of normal are the brighter em em The H the portions than Giotto II, show the interaction far Ha the show is "rocket to behind Moving II a seen ionizing WFPC2 The 1973). and images the of photoevaporative away (90 to which of At structure driving band fall all color region; sides, 3 X either Flow flow. has H as pointing the the to by background. employ column the images three OF were features almost in Ill, elephant itself AU) II this along green, with away clear close 10 of Society the with a 2 from Ha, the the of region. angle The Ml6 effect" shows Ml6 composite from in 15 energy The northwest and respectively. number shown radiation all image), kpc the of being interface, most neither Ha on earlier is can distance, M16 em morphological ionizing ionizing to from exclusively its three respect of outward I. a implication [S and the so flow to the (Humphreys are more fact of northeast a trunk the square comet an and II], on be front The prominent be deposition (e.g., in are driven side. flow incidence [0 They of the we interface columns • plane the work enlarge­ of that remains is seen seen and Figs. a flow of impor­ of [0 some­ where III] impli­ to visual struc­ Provided stars, stars. com­ face, these refer side, from stars root Hal­ Oort 1"= with The The mo­ the the are [0 III] the the off as on in of as to in to is 2 Bertoldi ture & lines II] sharp strongly emission edge The trunks to peak sharp from age It Moving well, profile peaks shows evaporative as rises broader scale then pressure from ionization -1.9X flow all interface terface this the where allow away lar and lar Howarth than to X (1993), Spitzer 10 The 3.2 rim. the This The narrow then extrapolate sn the Using by interest as type Ha is of halo procedure volume 17 is the slowly more is like the (cf. of height Bertoldi edge relief from - expected calculation Ionization halo, profiles all (Fig. the em is the Ha differences striking. the we 10 extremely displaced stratified the from from peak concentrated (1989). surface the line falls gradient forms [S seen 100 & Fig. unresolved that itself. but 16 1955; structure line nor from slowly acceleration of very assumed is conversion between conversion the Prinja II] in 4). flow Ha em. NASA falls emissivity of dense of AU the intermediate extinction Osterbrock stellar missing about seen in of 7a exponentially 1989). should this of peak. the as about The more surface sight from The McKee near the This the brightness also The [0 structure elephant the Structure normal until somewhat outside sight of with implied than prominent 3.2.2 thin (1989), among [S in density molecular 3.2.1 normal III] bright surface 2X that edges three the census Ha at through diffuse halos diffuse in shows To photoionization twice Astrophysics [S assumption be u] in Photoionization it low the Fig. of through region is is a et an at 10 Observed emission interface. II]. the [0 acceptable investigate to blends (1989), profile image of FWHM trunk present proportional lines regions can and between by al. 16 the the of lower rim of extremely up ionization profile to that 4 of the of However, the away a III]. density em as the with the the 1984). the from the same also bright images material. can total the to Ml6 that along outward, the mass tip [S the of structure (Fig. rises with Rather, ionization we elephant outside bright Photoevaporative in from the steep further overestimates interface A from resolution cloud. II] also be surrounding further [S [S emitting 1 a of dominates ionizing models location Hester in [S Ha estimate the polynomial from distribution The rim a cut sharp and peak, the as ionization seen of II] II]. 3); zone, in the column the to II] the I be Ha the [S Data In structure e rapidly as and in the a the of extremely from at background The the [S spectral trunks Ha Hillenbrand region rim, taken into II] seen photoevaporative in [S well. scale contrast, 1991 lines, zone seen [0 molecular then the the region profile, flux the rise as [0 II] of- three that Fig. rim. square II] [0 rim the II III] the the System the the and in interface III] emission [S as density fit through edge of falls in the right of In versus are zone. and in reaching of III] half of height 7a, [S type However, is Fig. interface, we emission bright 200 was well, the elephant is II] M16 Flow cloud addition the (Fig. thin the the and particu­ seen this neither density [0 root II] profile with longer which Fig. at a at cloud of peak, see [S et 2351 from 4 used flow AU. stel­ few PC. Ha im­ na­ and the but the III] the are the 2). the in­ [S al. in II] in as of of is to a 6 a a 1996AJ....111.2349H 2352 The The FIG. profile from the projection The ionizing with used using stars ionizing observed profiles 7. molecular © remaining the CLOUDY84 was with the (a) a HESTER American Kurucz effects. Observed flux radiation ionizing lightly were elephant Ha spectral cloud for brightness. extracted filtered ionizing ET profiles the (1991) is sources in to AL.: (Ferland e .!:::! -a:; Q ..!: "0 a.. ~ - trunks. .9 E ...... 0 ca Q) Q) Q) type (/) c:: nebula and the Ml6 Astronomical from of While HST 0.6 0.8 right 0.4 model smoothed 1.0 radiation the 05-6. the located 0 comes We 0 is ' Ha, IMAGING and 1993) this .·· Planetary ~ .... H with approximated ionizing ·.·.:-, 2 [S assumption to We X II reduce from a mostly n], to . 10 . Region distance • T=50,000 ... and Camera estimate compute 50 OF radiation T/10,000 Ha [S [0 [S [0 Ha n/2000 noise. a photons [0 Society is comes M16 single m] II] II] Ill] Ill] probably image. of (b) emission this is that the Distance K. Profile 6 X incident per 03-4 from The spectrum expected We valid the 10 • Photoionization second, along FWHM K showing 18 Observed Provided three from total then star. near em Along a cut the resolution the a --···- Flow .· model taken .... left. sharp edge ionization the tion ably agreement zones Profile ·.·' The Figure normal calculation edge, by offsets of of good. ::. Profiles matched density the reproduce .. the (em) the ···-;.·./···-··· it · .... to [S ··· overestimates structure 7b Model density the between In between .. n] profile · of NASA .. and photoevaporative particular :·· the presents the / Ha the ionization was observations. profile / of .. the profiles observations / observed ··: assumed the .- / Astrophysics the .. - the peaks the density / until structure interface, is sharpness interface result to -2.7X profiles of be in the the proportional of the and 10 position of the at adjusting outer 15 [S the the of photoevaporative em, this very tip II], Data parts the or model of calculation. to of well. Ha, 180 [S column of the the the the AU. II] System square and normaliza­ is As ionization flow zone The II remark­ interface. part in [0 root due 2352 [0 M16. The and III] m] of of to 1996AJ....111.2349H too shape evaporative of gave into variations the the the compared cm- of also ionization line geometry 2353 Allowing the which head extreme and cm- of thermal these pressure evaporation ably observed 3.3.1 is distance that the the (1990), extending distance 1983), ionization modeled M16 that parameters Shull stress flow, derstood netic sion set a The the The The ~ column modeling peak column. of three hard © observational Bertoldi relevant of the factor 6 work. 3 quantitatively is be from 2000 Photoionized of and [0 and field of pc. that physical & values ionization gives K. American the sight HESTER analogous observed considered work structure 3.3 dense and column pressure a of of the an of is McKee main as m] value the for the of (e.g., We in photoevaporative This case model. from directly em- Ha the structure of approximately at II strength, H the include ionizing halo. included This parameter of a the assumed dividing the & the parameters we dense emission ionization ~2 presented 30 least portions 11 estimate in typical has density columns emission through 3 McKee than parameters. is [0 of ET Cox II model the photoevaporative photoionization Regions head investigated at more is brightness structure, of at equation 1979). magnitudes to value only p/k=6X is a consistent good m] with several AL.: in elephant the shock any surface at the the spectrum characteristic 0.04 the and Astronomical density ionizing by 1972; in reasonable of profile, zone, of parameters. (Bertoldi extreme from the (1990). peak only the HST about structure here are considered agreement the tip photoevaporative measure and into that column as way Whereas 2 the swept 2 structures pc, velocity, interface X bright and The to flows 3.23 pc roughly Photoevaporative of of of 10 IMAGING calculations Raymond trunks were of the in shows 10 the the flow, of with the expression, and of in the a account spectrum. drove 7 from The flows the the column 17 than the in implication the ~4000 cm- factor observed of 1989) up extinction sensitivity which are fact II agreement from in might rim em expression dynamical extremely the particular this with while We molecular photoevaporative value given radius can be Ha by a being that the the column, as preshock hemispherical, outermost between determined the the 3 from photoevaporative is column that Bertoldi. K. for found OF gives model. well of II 1979; ionizing Bertoldi profile be radiative cm- bright about shocks Society cases For [0 the too of the of of This especially gives of geometry M16 2 flow quantitatively M16 modeled the the (Chini of determined is m] with Bertoldi 3 curvature rapidly sensitive soft a larger around structure uncertainties the t/J= p/k= that for in cloud the is Flows the at density, Dopita that 2" considered given The rim fact interface. in should parts zone can the Substituting by stars. is located the a the location a 10 the or & shocks the the the interior profiles & the predicted spectrum at far 1.4X 4 heads the that than with • in 0.02 out relevant that , head also varying case profile, simple. McKee 3 X density flow Kriigel too details physical (1989) of the photo­ photo­ which to Using of a Provided at prob­ emis­ 1977; more mag­ same flow way ram to at We 10 10 the un­ the the the the the pc, far the are tip be of of of to of of in in is a 8 5 a photoevaporative tion parameters density quantities medium tial strength flows, found emission M16 the based photoionized from low tively ter toevaporative that that will region how supports evaporative actually extension if observational However, the the molecular which the becomes shock, flow extend emission our image gestion Kennicutt the ascribed at dence 3.3.3 series most The least Having We In H by pv for field photoevaporative significance interior suggestion the we zones The leave much resolution extend 3.3.2 is II such the near that 2 per observations of a the in models providing above the can of further region of is of 4 X flow of present phenomenon suggest dominate photoevaporative of of into the HST from from the structure to Significance of such Fig. it cloud, correct. interior 1984) the the the se, the of to flows. argued the are suggests faint view the 10 clarify shock flow. smoothly is of NASA view the a crucial which the base later photoevaporative conclusion flow. image but 17 flow same molecular worth boundary emission itself the seen H 1 radiation as the out shock is the to is along photoevaporative em of of require and overall in the filaments, II physical Hester flows that the the not it of H that If, best of be suggestive papers is low the M16 still. H Hester this of regions. of that here is such sort the from is question of II noting the then photoevaporative evidence interface balanced is emission on offset Astrophysics away from away emission valid. similar emission II best in the region WFPC2. 30 interesting the M16 understood and fairly filling the from flow of idea this emission H of field. that The (1991) region. cloud, the to seems the undergoes flows their flow Galactic the diagnostics face et edges II the the described sharp, relevant that be in the As The technique concave other region from emission al. is in by closest occurs the of general. structures photoevaporative "ambient" task The by factors molecular the supporting and from comes strongly surfaces, from of flows, Looking the noted, secure moving, well-defined argues in assessing in (1991b) a columns (In considering location H of the the flow from to stratified peaks shock hand, the the as this fact of H determining ambient is II blister blister a beyond photoevaporative parameters speculate the near as features ''ambient'' a off II region nothing of developing shock toward of context be has itself.) blister Hester the for flow an shock, that density that photoionized a Data dependent regions, and of at throughout the cloud-in absence out such see and H of photoionized this concentrated out the of this H photoevaporative very the next H structure H different such II easily the this II pressure transition can majority striations to the what we arises the to II Stated in wall a interpretation. in that et II more interfaces. of idea. then regions region further ground the System the good regions. the surface distances situation include regions question al. the flow shock, see M42. pressure shock blister be suggesting flows shape of a appear of observed flow might H on edges the our between elephant than (1991a) broader simply, seen seen ioniza­ no ground overall II such photo­ poten­ comes a of of about based in are when these region (e.g., zone 2353 pho­ rela­ This blis­ may then then sug­ of H and evi­ We the the are the the the be in of of in in at to is II a a a 1996AJ....111.2349H eration of 2354 trunks, tip place pressure everywhere curvature, as tive the when rative pv pv interior nH rior'' west timate nebula state evaporative r tainly the extinction observed cm- II blister. photoionized away could general for is that ~ again more toevaporative flows tions HST ing trunks the trunks tures surfaces are 0 = 2 2 If Returning region llr dominated the rr=n; We 2 We of =Pif(r ambient interpretation emission the emission features. 1.2X 6 main © is of the pc 2 a constrain images from flow, it distant the on provide consistent along pc. of PCl might of HESTER have in located that because If zone might the limit (that are column American of 1 conclusion flow, diverges many through feature at (r the analogy the of 10 emission the column, after Ml6. nHrr=29 models the elephant P 0 0 the the corrected ram eroded 4. field 17 flow) in used lr) /r) if pressure on the the the is, conservation H to from y far By the show prove measure H EVAPORATING photoevaporative expect by a H flow em. small surface ionization consideration about the is 2 the 2 II II then of powerful Figure the ET seen the the pressure . , with ram the II II photoevaporative to three of the photoionized regions is the of where is based r the the Using is region. ionized AL.: parameters from cm- diverging region density away is the case numerous taken region trunks view. is only interior especially cometary in with the properties observations 30" reached pressure to emission our in Astronomical pressure divergence unresolved, of we nebula the from 10 columns. point the HST 3 see the of r largest the the front and to on ni of where suggestion about the to for 0 by shows Taking distance This ground-based makes 1 gas, in which to column is of the have IMAGING the be GASEOUS = elephant the of of H the nebula, photoionized that well that application as photoevaporation. the the the should 4000 fascinating of that globules be photoevaporative the of at a II the northwest measure flow useful bevto can observation flow these momentum small a the class 1700 flow. "ambient" a broader There photoevaporative emission of interior pv "ambient" radius region. whole defined the a of the but is revealed little shock drives r= number surfaces away nebula, II, stratification line em the 2 which that not trunks H fall =PHrr' from photoevaporative cm- of GLOBULES equations scale ionization where 1.4X The OF outside will for - protruding II flow. contribution are of is 3 of of image Society noteworthy the part from of in base of off the physical Since of M16 small-scale 6 regions. then dominated from photoevaporative interpretation sight of this shock flow curvature typically the the 10 as in of structure pc. the several the well ''ambient interior photoevapora­ approximately other requires shock density Since where of 18 these of M16 the of photoevapo­ the the to gives implies wall This H H T=8000 Indeed, upper simplify be distance of will the evidence flows, front, models, the the em over II paradigm II center models. Drawing from observa­ the elephant elephant to it interest­ used • regions region. PHrr regions objects has photo­ is of to of an of north­ by accel­ within in shock is argue when struc­ edge Provided inte­ pho­ flow cer­ that that and and this 10 the the the the the es­ the the the the an of of to to of is K H a 4 columns evaporative locations. many where in indicating tached these number umn umns, smooth. ephant from radii tive, this by properties filtered approximate histogram presented of globules rated near behind the necks rocket uncovered slowly trunks. stars, a .0 .0 o "5 z FIG. "' 0 E :J Ci Ol the Identifying the The Most hand 10- 15 by result subjectivity 5 especially I the of 9. the globules other indicating and/or to these images, lower in from that effect. trunks A as than Ha approximately morphology These of the Figure surface elongated I we which of columns, histogram of the in that Examples of of of and small as surface tie locations image globules dense their the identified these sizes. Fig. resolution NASA substructure the the gas pushed all (as and the and necks range near II them 6 numerous surface of that it globules small elephant distribution 9. around lower 500 shows of well and molecular The gas - in the measuring globules conical to the of seems the measured of are of point they from Fig. the back away a the 150 Astrophysics largest the 73 that molecular as smallest Globule bumps Histogram resolution reproductions. density few of these such an concentrated them 4.1 photoevaporative elephant a trunks themselves trunks that features, within 8 most globules r-~ AU, are lower or the "bumps" directly are to few enlargement by radii (Plate cloud objects are EGGs of drop-like are these regions 1000 objects is probably are radius the columns. along which being surroundings, the of appropriate detached of the driven of conical right over cloud the limit more the trunks was the surfaces 139), radii can indicated globules photoevaporation-driven away radii that (AU) the elephant globules photoevaporated (i.e., is features in include and 1000 The part n very structures of of off. suggest be columns set difficult of Data and are the or are surfaces M16 of bet) Working objects). the from seen, where 1500 their interface morphologies In by the of AU clumpy are of to these have very completely shown outline is measured in images. and Globules short, detected the trunks the column consider head the very that photoevapo­ the System in a including distribution to of protruding the irregular), resolution so of high objects elongated in radius. heads pick elephant they ionizing n at gas they subjec­ is Fig. of of are the photo­ Given that these more 2354 I. have very their pass 2000 col­ col­ that out de­ 8. left the are are el­ of In of A is is a 1996AJ....111.2349H further these have are clumps gation 2355 that s- from This lated toevaporative nebulae, eous other referee, formation. The ied M has EGGs M16-El number used years. "Ml6-En," stars census and of of concentrations greater -1 embedded lower ing EGGs would a of its Ml6-E3 visible the structure, a disk-like 10 cometary bright 0 1 In M16 By such this Visible column (Plate center. totally © ) 2 X - in (Bertoldi at few field a shown within by by are age Globules, the nomenclature found not in nebulae or comparing mass In the mass American that directly HESTER speed than of is than reveal star. at we associations, of is Hillenbrand various star Ml6 survive located we very relatively spirit particular, structures 10 140).] Ml6-E42, shown evaporated 6 X YSOs detached their of visible is The within stars the intermediate will I) appear in EGG 6 to YSOs. the about will Ml6-E52 3 of seen where 1989), years, for 10 near in time that the Fig. range or be a of additional from stellar of site 4.2 heads. refer molecular ET or - 16 There just authors in longer can the refer in 4 M 4 with the previous the the present. immediately and faint, 80 EGGs. em the are 10 to short-lived massive EGGs. AL.: Ml6 scales lOe. Star from seen, of n can Ml6 the and Fig. which obvious off the et from Astronomical 17 WFPC2 to as be 0 globules M be content due photoionization long tips is infrared to a are generally The (Fig. very al. . em than these HST distribution 0 well Also of Formation star mass WFPC2 the (down (e.g., be seen associated the [One the and these is detached lOa. . We examples for several cloud. of to names (1993) Following the bu 2.5X about and can fact from The noteworthy extended IMAGING most at interface lOd) stellar active about EGG as way. cometary has objects of see images shadowing small to structures. pre-main-sequence Bertoldi predict themselves. of upper This at by its features about be to several that M16 ages bright This be the images, its a these the is for more massive tip we a Hillenbrand seen number faint 10 recent in of with fraction is population one nebular tip. associated few of globule left using interface with is small other 200 4 has found and the of is EGGs that these to front structures, OF an 10 is & years regions ambiguous as in M16-E31 in because globules continuum Society Another comparable of surface Assuming YSOs of 5 recently pre-main-sequence the sometimes similar AU Jenkins behind that suggestion Ml6 the Evaporating elongated the and star The K the a shown examples condensations years the objects these several of of globules more after isolated and in K-band lower none containing indicates nomenclature et in a best ongoing few (e.g., order with with in of of radius, solar example at. rather the objects containing the been stars (Fig. to also 1992). structures in emerging complete instances column the source suggests a • are example M16 possibly cases to right appear­ (1993). conical 1 X masses Fig. the several propa­ in cluster of source calcu­ image 5 dense Provided mass) show stud­ large Gas­ pho­ (3-8 seen lOc). with than that Fig. star km 10 the top in in of 8. of of is at 6 a I leads evolve, densations where the which (1989). evaporation clumps on rates tive nebula regions cloud, emerge ionizing the terial eventually few cometary are are and EGGs the rated, slowly embryonic M16 those stars cometary (not in McCaughrean terms, well etary condensations. wavelengths ments, tified have something ''EGG'' (Garay (McCullough 1991; with As We In by In their concentrated EGG evolution M42 shadowing may of relatively front shown). et are YSOs. more a EGGs around disks;" identified PIGs, this particular, to the O'Dell may noted this examples contain emphasize them working the number al. the required are This 1987), including 4.4 (e.g., as which way is now sources eventually an (Fig. 4.3 globules have structure, remaining reaches section bump 1987), a about any have within externally an tail stars slowly Comparison proplyds, NASA do. and front above, obvious bump scenario (Mundy An it toward of Tauber et emerging. O'Dell especially et YSOs, and rare.) effect lld). embedded of of & is These in its (Fig. For to either al. also in al. are an the develops Evolutionary formed the other and and that we the features radio a the way explain "Partially similar continues have "proplyds" one than Stauffer on 1993; EGG. those pinch however, the 1995), Once globule supposed presented M16 tail forming of et As llc). et Astrophysics later ionized, we been Bok while consider et the suggestion is molecular contained structure objects h side the small into direction, al. al. continuum observed the al. its been with should apt depicted and have the O'Dell globules into diffuse EGGs star off. the Most observations in seen globules, to Due 1993), and 1994). the surroundings, we globule 1995). studied term. (Fig. 1994), nebular common Globules grew, to referred globule Ionized EGG them. the structure that Scenario and an (In will are unambiguous of front the do (an of in evaporate is most to EGGs YSOs cloud are and move & elongated for properties features radiation These ionization schematically Ml6 HST not with containing the llb), When are not seen the These relationship acronym images be considered Wen and and and These has face using very in totally condensations recently how itself know to cloud. exposed sometimes with already, presence completely Seen Globules" begin images of (Fig. for each of the Data through the in the the from are other been of using 1994). the externally the similar and relatively photodissociation in of may EGGs ionizing these has structure, similar field previously adaptive the what evaporated detached EGGs EGGs for in globule of evidence front name 11a), infrared photoevapora­ each As M42 stellar as objects. small which at so (Hester M42 System evolving or by at a globule, between been most "protoplan­ The of be in dense the within the fraction number millimeter in associated been structures begins the has phase shielded, many (Church­ implying in or Fig. Bertoldi multiple environ­ like objects, such sources quickly nebular appear- ionized evapo­ objects evapo­ photo­ due EGGs young which larger EGGs optics tip that et iden­ PIGs (e.g., 2355 been con­ well ma­ and the 11, the the its al. of of of of to to as of a for embedded ded FIG (EGGs) images globule, 1996AJ....111.2349H2356 . longer in 11. a Incident st®.v~~i«adJ,iAstltDBOtllieal in molecular leads HESTER An than t in M16 _> /\ the evolutionary Ionizing to ) . its _> (a) globule the surroundings. cloud t '1 A ET ~ Radiation formation dense * ' ' ' . AL.: ) it _> (b) will scenario * ~ ' 1 globule The v-vso HST first / (c) of globule Photoevaporative be a IMAGING This, for (which d) cometary c) seen Young from cometary b) EGG the survives a) combined from EGG approaches at Photoevaporation Photoevaporation may EGG evaporating takes stellar the molecular begins structure. shape OF contain Flow head against on ~iet~n.• object with M16 to globule of emerge cloud a emerges shadowing ga the photoevaporation (d) YSO) Front Front s eous structure If a is globule YSO Provide€~.~ embed- by . The the is s jects cussing for from cloud, Jenkins M42 this toevaporated. the pletely strong serve statement scales ous evaporating an condensations et M42, the to tion nebular ules, (1995). from ence ably a cloud The in globules ible is ionizations. What rily trend. Also ments the than the two range sponding 3-400 ance images less 200 may contour al. reasonable an The origin Our evaporating distance lifetimes a few argument point in nebulae YSOs. also M16 , AU than authors, well •teN seen M42, in be and to that the . the the is but evaporating ) few McCollough of 1993; The [between argument in 4.4.1 size we AU, destroyed, interpretation of The ionizing same the (1992) condensations. now the superficial in the side X for ionizing shows which our remains gave to as rejected into EGGs in is 1 in at . M42 times find similar 10 preventing Overcoming M42 limb Instead, as disks. The (A ASA from pc exactly evaporation the M42 O is M16 M16 well. the of a the 6 which suggestion and if says, including difference But ' compared in the us probably globule Dell smooth insightfully similar year for that the they smallest evaporation the us (O against sources surface differ M16 are brightened, , M42 10 objects the it can of sources a objects same lbl picture globule reopens it objects, This morphologies While Astrophysics . in ' why et to 4 the Dell globules, is more radii what they While the & roughly on recombinations larger age are of ionizing past years a/. M16, . enlarge objects see hard us from process model density Churchwell Wen idea objects the the , the population of neither not " O'Dell with et that found of of in the in obje suggested (1995) of from of an we informative overlaps their unless" (as a , located an to state, clouds al. M16 basis cloud M16 the objects where debate M42. appropriate has perspective the the times in cometary c proportional the exact M16 are they 1994), and tions a reconcile sources. opposed have the EGG such 1993; relationship distribution is clearly suggest representative agreement M42 in of objects globules been of found and EGGs cluster], is of "Unless seeing. reservoir model.'' probably their to are may just EGGs of However M42) in the with comparison as at of a about we Data the was et five that two evaporating near and condensations approximately characteristic O'Dell a elaborated collaborators look Bertoldi ours a objects a/ valid. They globules to traditional before seeing association be view this few objects that as that seen probably . distance owing the the times specific between EGGs fit McCollough seem the distances are to ?TSco, (1987) we thereby evaporating System similar A for of with at at inside to disparity , suggest objects the they d X nicely Orion In nature & disk in these this determined photoevapora­ 213 gas as they happen size work objects 10 the globules the further and to to and do between seen a M42 , Wen sizes evaporative 4 on Bertoldi the arguments considered are of where previously to paper objections the fit is difference molecular to objects the years M16 of posing , only are with PIGs radius typically into globules environ­ Jenkins' of in in by that needed, be (O'Dell the balance 2-3 nebular reason­ in the in similar around prima­ differ­ 1994). to of corre­ larger small M16. M42. glob­ com­ away et vari­ pho- time HST 2356 d dis­ live size vis­ and and this this ob­ ob­ are the the al. by pc of & in is a : 2357 FIG. M42 If against answered around evaporating embedded cation The cloud globules globule globule. EGG M42 reasons perspective, surrounding star side of ous in M42 tion to would nents nor proponents a orientations objects PIGs ponents embedded

the 1996AJ....111.2349H M16 Bertoldi be There In The ·········· aspect 12. authors is on differ argument with . a seems itself, If are this evaporating to revived uncovered of interface see globule 4.4.2 HESTER A the them are [the · @O.alffitliitia~lfu~ciWSW&f)ltiagftli{llvide~!fiy itself would viewed M42 · for of ···· present in principally several are sketch visible simply ratios by section EGG as · the ········~········ morphology inside halos Perspective . Further and of the M16. but to globule globule inconsistent seen disks. A the favoring as additional This must or the and the is reject the stars have is showing rather evaporating from is from ET Jenkins near its of of arguments EGG. that young we stars of t.lte edge-on The uncovered is we in difficulties burden disk of evaporating the actually AL.: M16 the shadow the model material in just the view an the model] stellar ionized more stars Visible the . have globules, we perspective an M16 projection how case Orion model difficulties direction When features argument HST of evaporating go the with object see Trapezium it YSO of evaporating would are perspective M16 the face-on, with shown be tail on not that data with ik picture disk arises IMAGING properties that from proof PIGs surfaces it for a not viewed a objects, from the to disk are through EGGs through and random seen rely disk. show have not these the against against say, valid, evaporating that one that with EGG as from totally now which the model. globule seen and therefore neither in be in H This of and been from must OF that "A disk that that nor side the evaporating cometary stellar-like the the from at M42 lies visible the the II similar distribution they young disks. propose the a destroyed. Ml6 least further • region/molecular dense historically on M42 evaporative objection picture a we have evaporated The M16 disk be long a model optical picture HST on with are stellar remains star (Fig more perspective their features Perspective addressed the have for if Rather, observed. model time distribution lead globules core object before images buried its they that . argument objects.'' M in globules over material associa­ identifi­ in 12), face-on of Once on propo­ is scales, 16 seen of which previ­ of M42. these cited were from flow pro- disk also and the the the the we in­ by an of is in a originally pated supposed evaporated externally Cullough evaporation. cally In modified model to pable by suggesting sponse of dard question column ing loss the typical that model used several embedded cannot et other limits it istence it idly 2000 them rare next radiation pected formation absorption Cullough a mates tent the termediate 10 cannot. significant shows 3 al. such Consideration This While The an penetrate HST objects the mass before this enough from with to extinction section by is plausible. of A that observations 1995) i~liW,.S'At envelope of is arises of be to dust find of globules on disk a magnitudes scarce argument of McCullough variant penetrating observations radiation a from we that <0 model, et (O'Dell et disks these the loss suggested disk the the to of disks ionized PIGs within steady reaching through and order theoretical from in that al al. infrared properties to from However, we . are planetary from raise 03 the be fraction upper . surface source external . M42 from the balance Hillenbrand curve (Seaton masses ( high observations around 1995). Using more which 1995) consider of would in M UV also an driven. of the the evaporated 10 state the does et surfaces ionizing consideration 0 will is the M42 the that N~HtS~~S~M (e.g., of the 22 an limit embedded by the mass the al. signatures of from for et M16 EGGs M16 of how observed 4 outside close generally. of version showing the visible systems em- photoevaporation . grounds, this embedded (e evaporating model disks-a Churchwell is 4.3 the stars if not be question the be al. they surface neutral the 1993; have . hypothetical The the g., on stars Stauffer disks subjected stars Disks same the ionized can mass of model stars? et 2 we attenuated imply observed to neutral the in Bohlin absorbing studied. question of 1979), must envelope al. in neutral extinction, been of ionizing evaporating find disk being McCollough (as in are cluster in a of that envelope are evaporating neutral of parameters of neutral result which loss observational of the (1993) The or disk. small that was M16. Orion the rare massive et throughout radiative et first disk the cited that how envelope by invoked to this evaporating et the the neutral from al. inconsistent globules al. obvious disks name of there shown by that environments al. source The non-ionizing the the embedded columns propagate any and Orion disk, noted Similarly, material. model column material disk M42 of (1987), as the 1994). be should (see a 1978) the evaporative disk may full disks evaporating in embedded evidence for can radiation "protoplanetary evaporated disk transport et factor globules. widespread drive to to is evaporation buried would that answer Fig. larger their PIGs. M42 PIGs of al. evidence is the force balanced be be account implies be disk In inferred model who and be model around gas. not Assuming has with disk. through it 1995) statistical 6 incorrect inconsis- the of globules no the volume. (Mundy is UV seen are be in Rather surface are in a picture behind for antici­ reach­ physi­ shows of is In In fairly order disks disks mass been stan­ 2357 light esti- able disk disk Mc­ Me- rap­ was The was that that ex­ ex­ ca­ the the the the for for re­ for in­ by by in is a , 1996AJ....111.2349H of if Perhaps Fig. AU there has majority when rounding bedded probably structures found a cated appear are detect disks is 2358 Working nebula view, we tures was small, sibly spread ered a left object derstood isolated tion that brightened, suth.as ficulties associated appear disks obviously and that the will making studied scarcity lOb), "proplyds" YSO. handful large a the We We We should early the very © a X behind M16-E42). not accretion be nebrilo$1ty.) 10d. such as against in disk-like are are along but an well faint a M16 insubstantial disks.) <150 existence can near conclude is to wish HESTER ·within American to in disks the discussed HST A small of HL given M42 disk-like of between of the good disruption EGG as·a in reflection emission. This intrinsically be further disks can are objects M16 of be third contain disks with see similarly the above surrounding Orion extended a the data 4.4.4 by the Tau to by disk-like the often isolated most images AU, are high the are not dark disk The onto also an candidate object these evaporating be evaporates them structures might head photoevaporation O'Dell left-hand disk embedded Hillenbrand disks ET around Summarizing of that background suggests (Stapelfeldt This present, EGG objects same structure uncovered M16 present. below PIGs are the very pass and feature and massive second nebulosity be compelling AL.: massive (The YSOs of object cometary address candidate of disks we might of is continuum Astronomical objects, also head rare. short (e.g., objects accretion object associated number, and explicit column outflow sort filtered is and do massive HST material 1100 M42 for fact in can seen edge they that seen influence is about located either a not demonstrates object within such disk Sec. coworkers. We the of lived. disks M16-E52 disks be of a M42. the disk IMAGING et prematurely that emission. it see looks et AU within circumstellar and a due in the Ml6/M42 can column show of is object al. version globules in II about taken evidence might cavity al. picture, also because few in question 5.2. stars as is in 80% absorption. circumstellar source the we with should (see inside column long is in Another opposite the near (e.g., to many environments (1992) M16. Most be M16-E52. photoevaporated. 1995), a emission disk M16-E52, disk-like Orion do find them. small either an might the great seen. as Fig. as and HST that go as objects comparison I. of In the There X OF embedded see our of M16-E1, evolution. it at that be of Society evidence of The the of comparison terminated This 500 originally against II the that bright contrast suggested on and the is Ml6 top lOb). EGG-like possibility conical are This may its PIGs disk deal The images nebula, be such disks edge-on the left and the In purely luminous, or we Ha are to best structures AU YSOs object of which center because disks object being might additional which EGGs, fact as behind, surrounding be (This implies M16 like is such as become a show are the three images in M16-E32, the to wide, reflection that relatively source. cases shown Evidence dark the of but a the • M16. that that that view in the field As labeled objects objects able uncov­ can in we be do that as is reflec­ is object EGGs wide­ is M16. plau­ Provided these case. what M16 such limb then em­ fea­ Fig. sur­ find 700 that that that and and this dif­ un­ not the are the for are we lo­ an be of in to of to If is It found rimmed evolve evaporating objects formation objects objects disks as long driven implosion However, PIGs, therein). tion toldi the Wen which because bright picture propagating Shchekinov servations fragmentation ephant images globules did in rgeig n self-limiting and triggering the the models point pelling supposed. star core-that determined This the the may such limiting In evidence The The Shu globules cloud, point by remainder class not formation and is be as time. (1994), 5.1 may (1989) that contrast, and 5. in contain H implosion into HST a competing trunk naturally argues seen offer are and case the are the associated lead clouds 1HE they Recent radiative very Elmegreen II seen of Triggered of it as leading a Rather, these of be wind the 5.2 (e.g., A also regions, bare, by Taurus applied. being coworkers observations of few globules, 1994). begins in star in that NASA EFFECT objects direct a to structures and the may appealing picture, M42 the good and/or of disks, against here masses Limiting in the M16leads self-limiting star the both containing work the seen eventually objects other accounts may the formation massive Sugitani in the of dark endpoint able implosion to if ideas Bertoldi stars be with evidence single to molecular formation may as Star and review formation regions nebulae. Star-Forming OF (1992). However, this the the cloud to in the M16 be on the produce some Astrophysics offering of objects to EGGs. (e.g., ovals 0 themselves. the which in M16, the of fact formation may important are Formation process of the be stars collapse support interpretation STARS disks. to for dark infrared & M16 core elephant triggered stops of Masses M16 aspects of & fact in process of of a In of circumstellar of basic that relatively Shu play embedded the induced cloud, Ogura description one found the currently On a of galaxies radiatively us some McKee more radiatively which the particular, clouds oval from because ON that are strong further are played we thermonuclear observed et a of a evolution physics the of a Clouds of beyond role sources of STAR of When single versus have al. close trunks prominent significant of in star see existing the the reported isolated of which the which 1994, surround Protostars by other includes this rare. considerable that of subsequent wind-an (1990). 1987) forming (e.g., infall it Data these a within relatively masses star formation dense FORMATION been of radiatively ionizing studies view says a driven the role disks. driven of star Disruption properties have process. it EGGs the these star contains of and While hand, is photoevapora­ clumps star was and boundaries by Carnmerer make ideas around in that star-forming as those members approaching role System star YSOs. that a fusion of Radiatively of reaches in been Two references O'Dell implosion implosion event of objects formation triggering few dissipates generally to generally few radiation HST both the M16. stars stars and isolated formed. The of interest in a can bright­ driven hasten within a EGGs of taken com­ for in M42 such such This 2358 Ber­ self­ HST star. that star ob­ the the the are are el­ be its of of as & & a 1996AJ....111.2349H question how cluster could 2359 YSOs toevaporation has have for M this rupted they nated stellar forming emerging, condensations cavity. of lecular Reipurth typical vational very rule. the show images could not to that termining these mass ronment they way ration photoevaporation strong (Fig. formation final diatively collapse, only ing guing masses tostars more winds, 16 It indicate The There It Regardless the determining small removed show © to question. the then is two big is If masses accreted were contain smooth when stars. lOb). EGGs accretion isolated be ample continue is within that consider winds by winds. objects HESTER environments apparent American with possible Shu cloud These a of in it YSOs of in reason is interpreted they driven directly stars are YSO 1991). conical it is then such outflows is M16. they M16. the of uncovered, greater that the leaves Further, Another whether the they et photoevaporation the that them a were evidence clear have the terminate objects; of the of As all environments objects If need with of al. final embedded associated couple freeze a in has appear prematurely, stars external to models to ET in implosion the that In disturbed the The which disturbed Shu's were dominant reflection those of whether expected, new responsible picture EGGs M16 a from are M16 suggest draw. isolation. anything disturbed contrast, AL.: (e.g., yet evidence that masses masses the the signature cloud to as is this the in such fact Astronomical the of may in to stars responsible uncovered. of be same the or a to ideas they show of any material fact HSTIMAGING that infall the stars photoevaporation disruption had exceptions numerous join YSO same of The with the that within mass Shu's environments within reach in structure as whether and star that nebula left environments be YSOs of process reservoir of that EGGs radiatively isolated or that the and were for stars other its finished Ml6. forming order about seamlessly for that locations none provides some most question these the the subsequent sitting formation whether basic stars hand prior distribution environment outflow EGGs ideas that we there in the which the determining can reach. near a forming In EGGs exceptions both than reviews have of so of to photoevaporation is the of to part. characteristic stars. see, for star are point star to they molecular of this picture in accreting be within are evidence doing the are be this the the in the OF driven a role they being where we gas then cavities that the It Society for smooth, correct, formation determining with yet seen and were in There way that view, M16 correct stars. over are star surrounding fragmentation M16 head EGGs of sorts could statement. in where are including from midst of Fig. was of were stimulating the have to also is in in isolation going that begin in the uncovered the implosion the forming of still they 70 forming are correct winds that mass of photoevapo­ the whether cloud. blow An is would of limiting the M16 responsible be which lOa, this for in addressing larger embedded spheroidal applies time they of masses EGGs molecular column prove no been generally accreting in structure "usual" the to. • obvious interest­ M16 WFPC2 with are stars a that One before means obser­ EGGs which termi­ strong in which stellar Provided in small often Most envi­ seem later. Pho­ have stars stars they pro­ mo­ dis­ just and and the but de­ the the the the ra­ ar­ do of in of in is II cloud its many the have protostar of grow. Hillenbrand basic Some significant still evaporative quantitatively observations cloud, a in WFPC2 the rative tions region. remove namical, principally structure from explain evaporating cometary overall gion mension massive tain the served forming disk gions. disk a EGG than YSOs the nomena shown structures flows 1991). physical number terms There Second, the Finally, way by cloud molecular elephant traditional YSOs. model to model been," modeling, similar stars of of is Once of is interface interpretation and cloud in We structural are For to In geometry the observations onto accrete much this of dispersing observations associated stars the exposed in them structure are of and forming 6. globules of cores M16 future are be paradigm result. in the physical see in example, M16 we SUMMARY for These responsible isolation, flow. an which et the recent gaseous NASA paradigm. three limb-brightened EGGs of were trunk from protostars. physically can ionization the regions cloud seen, of never al. understood pressure EGG report arguments little are these itself. seen the H their and work and provides the of This angle Such by (1993), main of have within seen objects, it II papers, which is structures often do material with morphology quantities these are the which evidence of here not suggests is will. region/molecular the emission ambiguity Scowen objects globules to the photoevaporation commonly of A full the Astrophysics AND we of description not uncovered, to either results on from objects of understood. region, While number implausible. for 30 globules for ufos from outflows properties the discovery determined it isolated as will be are many there implication we used us contain complement the which star as directly CONCLUDING is Doradus. that EGGs "premature" emerging remain cometary which terminating in rare. population with find et ionization a such for investigate line photoionization of or medium set. formation still the would were normally of to al. way and M16. of otherwise applied this can and "EGGs," may winds, no star YSOs, however, properties Even the a couples motivate as might density these of of (1996), they in Further, valid the need work. look by of forming. While Such their the best is cloud a from The YSOs globules be H generalize the formation. surrounding YSO's. of of Data population calculating REMARKS stratified of a are if that to jets, present structure are the II stellar in have this stars once infall to photoevaporation at be molecular its different relationship may the of natal observations First, a it objects. apply the these regions the probably surrounding a the viewed. an interface invoke larger known of in paradigm the the turns understood the will or surroundings, few physical, As of continued photoevapo­ the System that seen If M16 H mass evaporating evaporating content, have in we in material.'' other effect to masses ionization molecular this objects II When such a noted remain disk-like three implica­ of seen None out the H provide disks the process {Hester ''might regions in present to objects Unlike photo­ cloud, "have of found along differ small same II M42 2359 con­ with phe­ may H out­ that that ob­ dy­ the are the re­ re­ di­ by an to of as of in to is II a 1996AJ....111.2349H from any 2360 tion. the particular physical striking, also a and Bertoldi, Bertoldi, Baldwin, Chini, Churchwell, Cammerer Cox, Elmegreen, Dyson, Dopita, Bertoldi, Ferland, Bohlin, Garay, Goudis, Giuliani, Hillenbrand, Hester, Hester, Hester, Hillenbrand, Humphreys, Holtzman, Howarth, Kahn, Kennicutt, Tagle, bridge), Internal Astrophysics, 1991, 23, 613 106, number It In masses YSO © their D. 1364 provide is which R., F. 1906 conclusion, G. 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